compression Test Results

[lasturbo]

Did the burnt valve chunk that is missing disintigrated cuz I did not see any damage to the piston and wall in the pics?

[FuddyMucker]

No it didn't disintegrate, it luckily got blown out the exhaust manifold into the cat.
If it had fallen back in to the piston it could have destroyed the engine beyond economical repair

[FuddyMucker]

OK, just spoken to a Isuzu mechanic at the Isuzu main dealer for Exeter and he has checked on his system and can confirm that they are not stretch bolts on the 3.2.
In his dealer manual (which he won't let me have a copy of ) it says to inspect the bolts for signs of wear and replace if necessary. He also said that they have only ever done a hand full of 3.2 head gaskets but can't remember ever needing to replace the head bolts on any of them.

I'm guessing they only needed to move over to stretch bolts when they increased the engine size from 3.2 to 3.5

If I do need any he can order some in and post them out to me at £7.59 + vat each!

[FuddyMucker]

Picked up my new valve earlier (from a Frontera 3.2 V6) and Yes it is the same.



While I was in there I also asked them if they have a listing for headbolts?
They said they had nothing listed because they are not stretch bolts, I asked him how he could be so sure? and he showed me this..



Now I will be 100% happy to reuse the headbolts

[VX KAT]

Yer killin' me here...cuz I don't understand this stuff & I'm curious....what's a stretch bolt and why shouldn't you re-use the bolts? Already stressed? Is all that black carbon/soot "normal" or should those 1st pics posted be much cleaner?
OK, I could look this up on the intent but you all are more fun...

Newthings....My background is kinda similar to yours in failure analysis, except my expertise was in healthcare...investigating when medical things fail or go wrong....surgery, medications, instruments, human error....etc... so I'm like the National Enquirer.."Inquiring minds want to know".

And Fuddy can you trust that book? My mechanic has a reference book that says our 3.5 engine IS an interference engine...when the pros here says it is NOT.

[Moncha]

Ok, Kat, for the stretch bolt part, I'm gonna make you read something that was already written. http://www.gomog.com/allmorgan/stretchbolts.html This pretty much says it all.

The carbon on those/that head and piston actually looks pretty good. Thanks to fuel injections and computers. You will almost always have something left over after burning a fossil fuel, hence air pollution

We never said that it/they was a "stretch bolt"... On my side of the conversation, it's just common practice. Weak link of the chain kind of deal. Our machine shop figures that if the bolts have been through untold number of vibrations, wear, tear, heat cycles, over heat cycles, cool cycles, etc. Best practice is to replace.. The end decision will be yours.

Interference engines? Last thing I knew, the 3.5 was an Interference Engine.


Non-Interference


Valve/Piston Interference

For the most part, even if it wasn't an Interference, I wouldn't take any chances. I had a '88 Acura Integra 1.8 Non-Interference with 300k on it. Lost the timing belt, the was just enough carbon built up on the piston and valve that it cracked the head from the collision anyway. They may be non-interference from the factory but will it stay that way?

[Ldub]

http://vehicross.info/forums/showpos...7&postcount=21

[VX KAT]

Excellent! Thanks Scott! I totally understood the stretch bolt info.

Interference v. Non-interference? I'm still not sure...
Here's where I got some info:

http://www.vehicross.info/forums/sho...ference+engine (especially posts 20-24)
http://www.vehicross.info/forums/sho...ference+engine
http://www.vehicross.info/forums/sho...30&postcount=2
http://www.vehicross.info/forums/sho...4&postcount=50

[VX KAT]

http://vehicross.info/forums/showpos...7&postcount=21

Once again, great minds think alike... Or at least VX minds....

[Moncha]

Thank you dub, you and Sue have mastered the Search Engine

[FuddyMucker]

I have now run out of daylight
But have had a good day.
I have removed another exhaust valve for inspection



And going on the seat condition of the second valve I have ordered up a complete set, looks like it will be off the road a bit longer..........

[Ldub]

Thank you dub, you and Sue have mastered the Search Engine

Ain't none of it possible without you Boss......

[Moncha]

...And going on the seat condition of the second valve I have ordered up a complete set, looks like it will be off the road a bit longer..........

Wise choice

[SlowPro48]

Sooo.... is the pitting on the face an indication that this valve was in need of adjustment - or is there a leaking valve guide seal and what we're seeing are problems caused by oil coking? The one in the pic was wire brushed right? How about a pic of one before it's cleaned up...

[Moncha]

Indeed, the pitting is an indication of mal-adjustment. Once its this far though it is too late. Most importantly with exhaust valves is the need for them to close completely and correctly. The valves, especially the exhaust, rely on contact with the valve seat to cool by convection, in this case, that valve, whether it was a weak spring, guide galling, or gross mal-adjustment, the valve stuck open, causing hot gases to constantly blow by, thus overheating the valve, thus burning it, first causing the pitting then worse case scenario the valve head breaks.

The black on the dome of the cylinder in question in my guess is actually coolant coming from the leaking head gaskets. Not enough to show in the oil but enough to cause carbonization. I don't think there is enough oil to really cause a "coking" as the cylinder walls look to be in too good enough shape.